There are many different situation to use them。I just wrote some type of them。 1. “了 ” to emphasize some thing have already finished. same as “已经”(already) (in Chinese grammar，there are not any “tense”. we usually express tense by add some temporal adverbial) for example，“我吃了饭” “我已经吃了饭” both means “I have already had lunch” “我想想” means I need to think about it “我想了想” means I “have already thought” about it 2. “了” add it after a verb to from a adjective part which used to express a state or condition。 for example， “他死了” means “ He is dead " We usually use 好 in question to express the meaning "is the action finished？" There is a word “好了” usually means "finished some thing successfully"。usually it is used to answer the question For example, A said: ' 你做好饭了吗？' (Have you finished cooking?) B answer : '好了' (I have finished)

well, "了"and "好"in some sentences is the same meaning,like: i am full.in chinese, you can say:我吃饱了or我好了."了"is adv,when u use it,u need to use a verb,however "好" can be used as adv and verb.the have a lot of different meanings,like "我看完了"and "我看好了"their difeerence is the front prifers to say :i hve done it.the other means :i have thought it well.it is hard to say all about the differences,as u can see,in the above sentences "了" and"好"even can be used together.u can put down this question and feel it in the daily life. i suggest u can see the chinese cartoon because it is a good way to learn chinese ,if u see the movie or the other,u will find that it not a easy thing.